Toe Overlap

General cycling advice ( NOT technical ! )
PH
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Re: Toe Overlap

Post by PH »

MIB2020 wrote: they could at least offer the design of forks to assist me. I do like the sound of a twitchy front end , I am somewhat used to that with various motorcycles I have ridden over the years.

I'm not sure if there's a way to test that before committing. I had a bike with 12mm more offset than designed for, I didn't like it but it was rideable, not sure what 30+ would do, even if you could find such a fork.
slowster
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Re: Toe Overlap

Post by slowster »

531colin wrote:Some suitable numbers.....
71 deg 54mm offset
70.5 deg. 59mm offset

How about...
69deg 51mm offset
68.5 deg 51mm offset?

Those are the figures for Salsa's Fargo drop bar MTB. They use the 69 degree HA throughout the range, except for the extra small frame, which has 68.5 degrees.

The medium size frame has a ~650mm front centre measurement, and using Pythagoras I calculate the front centre measurement for the extra small frame is ~614mm. Moreover the reach on the extra small is only 350mm, although I think that the relatively high stack of 594mm makes that figure somewhat deceptive (i.e. if it instead had a lower 558mm stack like the 50cm Elan, the reach would be longer, but crucially I presume still significantly less than the Elan's 380mm, and likewise for pretty much every other brands' bikes in that category).

I suspect that the Fargo's steering geometry might be dependent upon very wide tyres (to offset a relatively low trail?), whereas the Elan and similar bikes are often marketed on the basis of being able to take narrower tyres for road use, e.g. 32mm. However, whenever I read owners' comments about that type of bike the focus almost always seems to be a) on how wide a tyre will fit, with 40mm being a minimum and many wanting to fit 47mm or even more, and then b) insufficient clearance for mudguards with the preferred width of tyre.

If suitable 50mm offset forks are starting to become available, I wonder if it would be worthwhile Spa getting a couple of prototype frames made for an Elan style bike, but copying the Fargo geometry for the medium and extra small sizes, and then seeing what you and the other test riders make of them.
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531colin
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Re: Toe Overlap

Post by 531colin »

slowster wrote:...........
How about...
69deg 51mm offset
68.5 deg 51mm offset?

Thats a lot of trail.....getting into noticeable "wheel flop" territory, I suspect. https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry

slowster wrote:Those are the figures for Salsa's [url=https://salsacycles.com/bikes/fargo/2020_fargo_apex_1Fargo drop bar MTB[/url]. They use the 69 degree HA throughout the range, except for the extra small frame, which has 68.5 degrees.

The medium size frame has a ~650mm front centre measurement, and using Pythagoras I calculate the front centre measurement for the extra small frame is ~614mm. Moreover the reach on the extra small is only 350mm, although I think that the relatively high stack of 594mm makes that figure somewhat deceptive (i.e. if it instead had a lower 558mm stack like the 50cm Elan, the reach would be longer, but crucially I presume still significantly less than the Elan's 380mm, and likewise for pretty much every other brands' bikes in that category).

Well, yeah. For Elan, I'm stuck with 45mm offset for a carbon fork, and not too far from 72 degrees for sensible steering. If you go longer offset and very much shallower head angle then you are obviously shooting for short top tube and toe clearance.....but I'm all out of fairy dust! ....to sprinkle over it to make the steering work.

slowster wrote: I suspect that the Fargo's steering geometry might be dependent upon very wide tyres (to offset a relatively low trail?), whereas the Elan and similar bikes are often marketed on the basis of being able to take narrower tyres for road use, e.g. 32mm. However, whenever I read owners' comments about that type of bike the focus almost always seems to be a) on how wide a tyre will fit, with 40mm being a minimum and many wanting to fit 47mm or even more, and then b) insufficient clearance for mudguards with the preferred width of tyre.

If suitable 50mm offset forks are starting to become available, I wonder if it would be worthwhile Spa getting a couple of prototype frames made for an Elan style bike, but copying the Fargo geometry for the medium and extra small sizes, and then seeing what you and the other test riders make of them.


Well, Fargo is high trail. You can get used to all sorts of steering feel; but the steering feel is imparted by (1) tyre drag....thats the force which is trying to keep the steering centred; and (2) trail....thats the lever through which tyre drag acts. So I would think that if you fit a big draggy tyre, then you need short trail to counterbalance it and get the steering back to "neutral" ....shades of Jan Heine with short trail and fat tyres.

It would be much cheaper and quicker to just buy a Fargo and see how it rides?
One reason I got a Longitude was to try the steering, before I even think about wishing it on paying customers. Longitude is 68deg 50mm offset. Thats "modern" mountain bike geometry....to get the front wheel way out in front, so you don't take a header over the front end. Designed to be ridden with flat bars and a very short stem, I will be riding it with bullbars because I don't have a choice. I'm fascinated that "modern" mountain bike geometry is all going for high trail/slack angles, but "Gravel" bikes seem to be sticking with "road" steering geometry. I'm assuming that my Longitude (when I finally get it built) will be very stable on stony tracks; as I get older and slower, a major problem I have is the front wheel getting bumped off line and being unable to recover.
Don't get me wrong, I love my Elan; but if I'm brutally honest, I prefer the steering on stuff like Spa's Tourer (and roughstuff) and Wayfarer.
45mm offset is classically paired to 72 deg head angle, to give fairly bright steering on narrow tyres; you can slalom the cats' eyes no hands, but for me its too easily deflected by random inputs like wind or camber, or me not looking where I'm going. Half a degree shallower just makes it a bit more forgiving of the random inputs, but its just fractionally less sweet steering....its impossible to explain; the Tourers just go where I want seamlessly, apparently requiring no input from me at all. My daughter talks about riding her favourite pony (now too old) where she just thinks "canter" and they would canter.....whereas with a different pony she has to remember to actually ask for canter using her hands and feet (or whatever they do).

I suspect I may be a bit on the fussy side regarding steering geometry. I also suspect people are more influenced by fashions in tyre size than by any objective need. I have done most of my roughstuff on nothing bigger than 35mm original Marathons with the kevlar, and plenty on 28mm tyres. I have some 47mm tyres now, but I still can't ride stuff on them which I used to ride on 28s. Ho hum! I mainly use just one size up (40mm) to compensate for deteriorating vision and reflexes.
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RickH
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Re: Toe Overlap

Post by RickH »

I thought I'd throw in a comment purely because I'd had the page open for another topic so had a look at the specs for the Kona Libre.

It has a 50mm offset 410mn long carbon fork (with triple bosses, which was what I was looking for an example of originally) & 71° head angle (70.5° on the smallest sizes), front centre of 628mm on the 54 size. Runs 45mm tyres as supplied.

Make of that what you will. :D

By comparison, & if I'm reading it right, my 2016 Kona Sutra, with the same head angle & fork geometry, has a front centre of 613mm & I get slight mudguard, but not tyre, overlap. On the few occasions I get contact (with my size 10s) it is little enough that the guard just pings out of the way.
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531colin
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Re: Toe Overlap

Post by 531colin »

RickH wrote:I thought I'd throw in a comment purely because I'd had the page open for another topic so had a look at the specs for the Kona Libre.

It has a 50mm offset 410mn long carbon fork (with triple bosses, which was what I was looking for an example of originally) & 71° head angle (70.5° on the smallest sizes), front centre of 628mm on the 54 size. Runs 45mm tyres as supplied.

Make of that what you will. :D

By comparison, & if I'm reading it right, my 2016 Kona Sutra, with the same head angle & fork geometry, has a front centre of 613mm & I get slight mudguard, but not tyre, overlap. On the few occasions I get contact (with my size 10s) it is little enough that the guard just pings out of the way.


71 deg head angle and 54mm (2 1/8") offset is historically a widely used steering geo. for touring bikes....various incarnations of Dawes and Ridgeback have used this geo, but both of those manufacturers change the geo. as often as the paint colour.

The 2 Kona bikes are a pretty different shape. Libre has much more of a slope to the top tube. I haven't gone to the trouble to work out which size of each would fit me, but just to take your examples. (I'm using the Sutra numbers off the website; may have changed since 2016)
54 Libre FC 628 reach 386 stack 610
52 Sutra FC 613 reach 385 stack 568

Again, I haven't done the trig., but on the Libre, the front wheel is 15mm further away from the BB ; but the stack is much bigger; you are going 42mm higher up the steerer before you find the top of the top tube, so the top of the top tube will come back "a bit".....I'm prepared to believe that "bit" is 15mm. ....ie. the difference in FC., or how much further the front wheel is from the BB.
So how do you want to size your bike? Probably not seat tube length. Stack? Or bar height if you are comparing bikes with steel vs. carbon steerers? Frame reach without considering stack is about as much use as top tube length without considering seat tube angle. Bar reach would be good, but it isn't used.
MIB2020
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Re: Toe Overlap

Post by MIB2020 »

Sorry for the delay, talking to Sonder they assured me their new Camino in medium has eliminated toe overlap. The current web site still shows the outgoing models geometry but all new orders will have the new frame. The only issue now is I can’t order one ( top spec Ti ) as they are so overwhelmed with existing orders.
I have replaced and modified mudguards on my Ribble to make it a little better, just have to live with it this year.
slowster
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Re: Toe Overlap

Post by slowster »

MIB2020 wrote: 5 Apr 2021, 1:05pmtalking to Sonder they assured me their new Camino in medium has eliminated toe overlap.
Did they tell you what the front centre measurement is? Did you ask them what it is?
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Re: Toe Overlap

Post by MIB2020 »

They only said the current model has limited toe overlap for a size9 winter boot but it has been designed out of the new model and details will appear on the web site as soon as they catch up with backlogs.
slowster
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Re: Toe Overlap

Post by slowster »

MIB2020 wrote: 5 Apr 2021, 4:53pm They only said the current model has limited toe overlap for a size9 winter boot but it has been designed out of the new model and details will appear on the web site as soon as they catch up with backlogs.
You stated that the front centre measurement of your Ribble was 595mm and you wanted "50mm ish" more clearance than that. By my calculation the front centre measurement of the Camino medium frame based on the geometry currently on the website is ~603mm.
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Re: Toe Overlap

Post by MIB2020 »

Hi, yes but also I am going to a Medium frame, something in my opinion Ribble should ha e discussed with me as they were aware I was new to road/gravel. Don’t worry I haven’t ordered anything yet and it’s possible the shops will be open soon , try before you buy .
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CJ
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Re: Toe Overlap

Post by CJ »

531colin wrote: 1 Feb 2021, 1:15pm Some suitable numbers.....
71 deg 54mm offset
70.5 deg. 59mm offset
My Holdsworth Mystique gravel bike frame, that I chose as the basis for a clubrun/audax style of bike in order to get actual (not just pretend) mudguard and toe clearance in carbon, has 71° & 50mm, so 67mm of trail. That's more than I'd have thought ideal, a LOT more than the Thorn Audax it replaces (72° & 55mm = 52mm) and did feel very different at first, but not a problem and now seems just normal. I guess it's good to have more trail when using low-drag tyres, as I aim to do always but especially on a clubrun bike (28mm Conti GP4000).

When I designed a small titanium touring frame and fork for my wife I specified (and got) 70° & 60mm, so 63mm trail with 37-622 tyres. She's delighted with it, finds it steers better than most of the bikes she's ever had. She normally finds U-turns scary, but did one with her first down-the-street-and-back trial of the new bike. I was mightily relieved! Getting a frame expensively made to an untried design for your partner: that's really scary!
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MIB2020
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Re: Toe Overlap

Post by MIB2020 »

The whole toe overlap thing is becoming a hot topic to gravel bike designers, I have talked to a few manufacturers recently. They are aware it’s an issue off road and it’s definitely an something to discuss with potential buyers. Not sidestep the issue as Ribble did to me.
Would be nice to ride 2 bikes back to back (one with no overlap) on a proper off road circuit to see what the difference is, I really think the average leisure rider wouldn’t miss a slight lack in “performance” when gaining so much flexibility in using the bike.
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Re: Toe Overlap

Post by slowster »

MIB2020 wrote: 14 Apr 2021, 7:36pmI have talked to a few manufacturers recently. They are aware it’s an issue off road and it’s definitely an something to discuss with potential buyers.
How many of those manufacturers include the front centre measurement in the frame geometry details on their websites?
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531colin
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Re: Toe Overlap

Post by 531colin »

CJ wrote: 13 Apr 2021, 6:17pm
531colin wrote: 1 Feb 2021, 1:15pm Some suitable numbers.....
71 deg 54mm offset
70.5 deg. 59mm offset
My Holdsworth Mystique gravel bike frame, that I chose as the basis for a clubrun/audax style of bike in order to get actual (not just pretend) mudguard and toe clearance in carbon, has 71° & 50mm, so 67mm of trail. That's more than I'd have thought ideal, a LOT more than the Thorn Audax it replaces (72° & 55mm = 52mm) and did feel very different at first, but not a problem and now seems just normal. I guess it's good to have more trail when using low-drag tyres, as I aim to do always but especially on a clubrun bike (28mm Conti GP4000)................
I would find that unpleasantly twitchy....not relaxing at all
CJ wrote: 13 Apr 2021, 6:17pm...............

When I designed a small titanium touring frame and fork for my wife I specified (and got) 70° & 60mm, so 63mm trail with 37-622 tyres. She's delighted with it, finds it steers better than most of the bikes she's ever had. She normally finds U-turns scary, but did one with her first down-the-street-and-back trial of the new bike. I was mightily relieved! Getting a frame expensively made to an untried design for your partner: that's really scary!
We are in agreement, within half a degree.....but I did prototype!
I think U-turns are all about confidence; I can think of 3 possible confidence-inspiring changes with that bike...
lack of overlap
calm steering
(potentially) better weight distribution
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CJ
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Re: Toe Overlap

Post by CJ »

531colin wrote: 14 Apr 2021, 8:58pmI think U-turns are all about confidence; I can think of 3 possible confidence-inspiring changes with that bike...
lack of overlap
calm steering
(potentially) better weight distribution
Lower bottom-bracket (to suit 165mm cranks and shorter legs) so she can actually get a toe to the floor - like an average height male expects to - surely helps in that regard.

Most small women's bikes have not only toe overlap, but also ridiculously high bottom-brackets, and I think that's one reason so few women become really confident cyclists. With experience one can overcome that hurdle - all MTBs have high pedals for good reason - but if your first 'good' road bike worries you about falling if you stop, it takes unusual courage to gather the necessary experience.
Chris Juden
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